Example 2: For a field pumping test, a well was sunk through a horizontal stratum of sand 14.5 thick and underlain by a clay stratum.Two observation wells were sunk at horizontal distances of 16 m and 34 m respectively from the pumping well.The initial position of the water table was 2.2 m below ground level.

At a steady-state pumping rate of 1850 litres/min, the drawdowns in the observation wells were found to be 2.45 m and 1.20 m respectively. Calculate the coefficient of permeability of the sand.

Solution:

q = 1850 litres/min =

   r₁ = 16 m
   r₂ = 34 m
   h₁ = 14.5 - 2.2 - 2.45 = 9.85 m
   h₂= 14.5 - 2.2 - 1.2 = 11.1 m

   k =   = 2.82 x 10^-4 m/s  = 1.41 x 10^-2 cm/s